The instant invention relates to a process for the spinning of fiber material which is subjected to prestretching in a drafting mechanism and to main stretching (i.e., drafting), and which is then spun into a yarn by means of a pneumatic torsion device, as well as to a device to carry out the process.
In a known device the fiber sliver to be spun is stretched to the desired thickness by means of drafting equipment and is then spun into yarn by means of a pneumatic torsion element (DE-OS No. 2,722,319, corresponding with U.S. Pat. No. 4,124,972; and EP-PS No. 0,131,170 corresponding with U.S. Pat. No. 4,565,063.) The yarns spun with such a device are low-bulking and also fail to attain the strength and uniformity of ring yarns. For this reason they are only suitable for a limited range of application.
It is the objective of the instant invention to create a process and a device of the type mentioned above, by means of which high-bulking, soft yarns of a character similar to that of ring yarns can be produced in a simple manner.
This objective is achieved according to the invention in that in the course of stretching, the fiber sliver is gathered together to a minimum width which is at least approximately 1.5 times the diameter of the torsion element, and in that the fiber sliver is not gathered together any further after this first gathering together before being subjected to torsion while said diameter is maintained. It has been shown that controlled spreading of the outer fibers is thus achieved, said fibers looping around the yarn core during the subsequent twisting process so that when the false twist to which the yarn core has been subjected is untwisted these outer fibers are on the one hand incorporated into the yarn core, while on the other hand however, not all of them surround the yarn core with the same density. In this way a hairy and high-bulking yarn with the character of a ring yarn is produced. The fiber sliver is preferably gathered together to its minimum width during pre-stretching, immediately before main stretching. The minimum width should not be more than approximately 2.5 times the diameter of the torsion element. In this way, high spinning speeds can be achieved. It has been shown that the degree to which the fiber sliver is gathered together as it enters the pneumatic torsion element is decisive for the way in which the outer fibers will loop around the yarn core during spinning. In order to maintain control of the relationship required for this, the fiber sliver is gathered together, before entering the pre-stretching phase, only to a width which is greater than the width to which the fiber sliver is gathered together before entering the main stretching phase, in preparation of the entry into the pneumatic torsion element. Gathering the fiber sliver together before it enters the pre-stretching phase to a width which is approximately 1.3 times the width before the main stretching phase has proven to be especially effective. Stretching should be minimal while the fiber sliver is gathered together to the desired minimum width so that this process can be controlled more effectively. To achieve nevertheless a high degree of overall stretching, the pre-stretching phase is divided up, with the first pre-stretching being stronger than the second pre-stretching. Stretching between 1:1.1 and 1:1.5 has been shown to be especially advantageous during the second pre-stretching phase.
The fibers which are spread away from the fiber material leaving the drafting equipment have a tendency to catch, through adhesion, on the normally rubber-coated upper roll of the outlet cylinders of the drafting equipment. It has been shown that these fibers can also easily be fed to the torsion element if the fiber material leaving the drafting equipment has been deflected from its previous conveying plane n direction of the upper roll.
To carry out the described process, a device is used in which the width of the condenser before the main stretching field measures in accordance with the invention at least approximately 1.5 times the diameter of the pneumatic torsion device which has the same diameter in its injector component as well as in its torsion component, from its intake opening to its outlet opening. This configuration makes it possible to build a simple device which furthermore produces the desired, high-bulking yarn, similar to ring yarn. To obtain this spinning result it is also essential that the pneumatic torsion device be at a defined distance from the clamping line of the feeding cylinders of the drafting equipment. The intake opening of the torsion device is therefore located in the nip zone of the pair of feeding cylinders of the drafting equipment. Preferably, the intake opening is located in the tangential plane touching the feeding cylinders.
To incorporate the fibers which are caught due to adhesion on a rubber-coated upper roll of the pair of outlet rolls of the drafting equipment, it is advantageous if the intake opening of the torsion device is offset against the conveying plane of the fiber material in direction of the upper roll.
It has been shown that the strength of the yarn can be influenced favorably by providing notches at the intake into the torsion device, whereby said notches, in a preferred embodiment of the invention, are constituted by the intervals between teeth of an internal toothed ring.
It has been shown that by adapting the angle of inclination of the compressed air channels of the injector component in relation to the axle of the torsion device it is possible to influence the hairiness of the yarn.
According to invention it is therefore possible to provide for this angle of inclination to be increased as the width of the condenser before the main drafting field decreases in size.
To produce soft, hairy yarns it has furthermore proven advantageous if the air pressure in the compressed air channels of the injector component can be controlled in function of the spinning speed, in such a manner that it is lower at higher spinning speeds than at lower spinning speeds.
It has been shown that the best spinning result is achieved when the distance between the compressed air channels of the injector component and the compressed air channels of the torsion component measures from 30 to 40 mm. It is furthermore recommended that the pneumatic torsion element be selected so that the size of the injector nozzle outlet portion defined by the distance between the compressed air channels of the injector component and the clearance between the injector component and the torsion component decreases as the spinning speed drops. In this case the relationship of the lengths of the injector nozzle outlet portion and of the torsion nozzle intake portion is a function of the spinning speed, and is preferably from 1:4 to 3:1.
In order to achieve an optimal effect even when low overpressure is fed to the pneumatic torsion device, the face of said torsion device pointing away from the drafting equipment forms a sharp-edged right angle with the bore of said torsion device in a further embodiment of the invention.
In practice, ring-type yarns are desired which are characterized by their softness to the touch and by their hairy appearance. Such yarns could not be produced until now with spinning devices in which the yarn is produced by means of a pneumatic torsion device. By means of the process and of the device according to the instant invention, this short-coming is eliminated. At the same time the high-bulking character of the yarn can be influenced in many ways without detriment to yarn strength or to economy.